Editing Setting:Brighthammer 40,000/1st edition (section)

=== Tyranids ===
Hailing from a remote world perhaps not even located in the Milky Way Galaxy, the Tyranids were first encountered on the Imperial world of Tyran, thus earning their namesake.  The Imperium's initial contact with the Tyranids was relatively peaceful, though Imperial diplomats were somewhat unnerved by the aliens' bizarre appearance and oddly-designed ships, and communication proved difficult even with the aid of a psyker translator.  The Tyranids seemed to sense this unease and very politely requested to take DNA samples from the lifeforms of Tyran in order to further their research.  After some negotiation, the humans agreed, and the Tyranids promptly left, seeming to disappear from the galaxy without a trace. 

Nearly 200 years later, the Tyranids returned in the form of a "Genesis Fleet," a large convoy of living starships that seeded barren worlds with bizarre and beautiful forms of life.  Wherever this Genesis Fleet went, dozens of meticulously crafted biospheres were left behind, each largely hospitable to humanoids and full of fascinating wildlife and ecosystems.  The Tyranids left a trail of "Eden Worlds" behind it, each more exotic and fascinating than the last, until the Genesis Fleet finally met with Imperial diplomats once again.  Taking new human-like forms, the Tyranids' diplomats explained that they were a race of bioengineers and terraformers seeking to study the life-forms of the universe and use their genetic data to create the perfect planet, and that the Eden Worlds were attempts that didn't quite meet their exacting specification.  After additional negotiation, the Tyranids were granted the right to populate select desolate worlds on the outskirts of Imperial territory however they saw fit. 

While most prefer to travel with the Genesis Fleet, a few Tyranids have settled in the Imperium, taking forms more familiar to humanity by mixing its DNA with their own.  These Tyranids find great success in serving as botanists, naturalists, or ecologists, but some make use of their race's mastery of the double helix.  These so-called "Gene Merchants" collect genetic data from plants, animals, and citizens, using their bio-wizardry to cure diseases and maintain the balance of local ecosystems, making them natural allies of the Agrarium of Mars.  Some Gene Merchants have reportedly ensconced themselves in Space Hulks, cultivating gardens and aviaries while fighting off space pirates and hostile aliens as they try to modify the derelict spaceships to provide aid to stranded or wayward travelers.

Sadly, the time of the Tyranids may be ending.  The Genesis Fleet will soon complete its journey across the galaxy, and unless some incredible new life-form is added to their genetic banks, the aliens will likely begin the long, silent voyage to another galaxy as they continue their never-ending quest to build the perfect world.  The Tyranids will leave behind hundreds of miraculous Eden Worlds as their legacy and gift to this galaxy, as well as those of their race that have chosen to live among humanity.